301467-005 Datasheet, PDF (241/426 Pages) Intel Corporation – Express Chipset

Functional Description
R
12.6.4.4
12.6.4.5
12.6.4.6
two vertices attribute values thereby creating the correct flat shading terms. This condition is set
up by the appropriate state variables issued prior to rendering the primitive.
OpenGL and D3D use a different vertex to select the flat shaded color. This vertex is defined as
the “provoking vertex”. In the case of strips/fans, after the first triangle, attributes on every vertex
that define a primitive are used to select the flat color of the primitive. A state variable is used to
select the “flat color” prior to rendering the primitive.
Gouraud shading is performed by smoothly interpolating the vertex intrinsic color components
(Red, Green, Blue). Specular Highlights (R,G,B), Fog, and Alpha to the pixel, where each vertex
color has a different value.
All the attributes can be selected independently from one of the shading modes by setting the
appropriate value state variables.
Color Dithering
Color Dithering helps to hide color quantization errors. Color Dithering takes advantage of the
human eye’s propensity to “average” the colors in a small area. Input color, alpha, and fog
components are converted from 8-bit components to 5- or 6- bit component by dithering.
Dithering is performed on blended textured pixels. In 32-bit mode, dithering is not performed on
the components
Vertex and Per Pixel Fogging
Fogging is used to create atmospheric effects (such as low visibility conditions in flight simulator-
type games). It adds another level of realism to computer-generated scenes. Fog can be used for
depth cueing or hiding distant objects. With fog, distant objects can be rendered with fewer
details (fewer polygons), thereby improving the rendering speed or frame rate. Fog is simulated
by attenuating the color of an object with the fog color as a function of distance. Higher fog
density produces lower visibility for distant objects. There are two ways to implement the fogging
technique: per-vertex (linear) fogging and per-pixel (non-linear) fogging. The per-vertex method
interpolates the fog value at the vertices of a polygon to determine the fog factor at each pixel
within the polygon. This method provides realistic fogging as long as the polygons are small.
With large polygons (such as a ground plane depicting an airport runway), the per-vertex
technique results in unnatural fogging.
The GMCH supports both types of fog operations, vertex and per pixel or table fog. If fog is
disabled, the incoming color intensities are passed unchanged to the destination blend unit.
Alpha Blending (Frame Buffer)
Alpha Blending adds the material property of transparency or opacity to an object. Alpha
blending combines a source pixel color (R_SG_SB_S) and alpha (A_S) component with a destination
pixel color (R_DG_DB_D) and alpha (A_D) component. For example, this is so that a glass surface on
top (source) of a red surface (destination) would allow much of the red base color to show
through.
Blending allows the source and destination color values to be multiplied by programmable factors
and then combined via a programmable blend function. The combined and independent selection
of factors and blend functions for color and alpha are supported.
Datasheet
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